The second category uses the FLOW-based approach [1]}, [2]}, [3]}.
The FLOW mechanism is proposed to incorporate intermediate representations generated during the process of answering previous questions. Compared to the approaches that simply append previous QA pairs to the input question as input, FLOW integrates the latent semantics of dialog history more deeply. The first FLOW-based CMC reader, called FlowQA [1]}, achieves state of the art on CoQA and QuAC when it is published.
